This section provides background information related to the present disclosure which is not necessarily prior art. This section also provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.
Currently, the United States collectively spends on the order of a trillion dollars annually on electricity for lighting alone—in fact, a quarter of most buildings' electricity usage is for lighting. Thus, even a modest increase in lighting efficiency can result in tremendous money savings and benefits to the environment. Solid state light emitting devices (LEDs or organic LEDs) potentially can replace existing incandescent and fluorescent lamps as a more energy-efficient lighting solution, offering luminous efficiencies in excess of 100 lm/W.
However, the cumulative cost of lighting comprises not only the electricity cost, but also the cost of the lamp. To be commercially viable, any emerging solid-state lighting (SSL) technology must simultaneously become both cost- and energy-competitive with fluorescent, high-intensity discharge (HID), and current LED-based lamps. Thus far, LED-based lighting has not been cost-competitive in most markets (e.g. indoor general lighting).
Importantly, in addition to luminous efficiency and cost-effectiveness, to facilitate widespread adoption, the lighting quality (i.e. the color rendering index (CRI)) must also compete with that of traditional incandescent and HID lights (typical CRI >90). Backward-compatibility with existing lighting fixtures (e.g. fluorescent lighting fixtures and Edison sockets) is also highly desirable. To date, virtually none of the emerging light sources satisfy these requirements.
Inorganic white LEDs can potentially satisfy SSL requirements and exhibit device lifetimes greater than 50,000 hours. To date, InGaN and AlInGaP based LEDs have achieved power-conversion efficiencies exceeding 50% in the blue and red wavelengths, respectively; InGaN based green LEDs have efficiencies of 30%. Due to expensive manufacturing processes (e.g. epitaxy) and non-compatible blue/green and red LEDs materials, current white LEDs are predominantly based on blue LEDs coated with yellow phosphors. This approach, however, generates very poor CRI output (ca. 70). In addition, each LED die size is only on the order of 1 mm2 or smaller. Hence external lens and diffusers are required, which lead to additional manufacturing and assembly costs.
Similarly, white OLEDs are potentially capable of satisfying SSL requirements, offering superior control over the emission color, with a theoretical power efficiency exceeding 150 lumens/Watt. To date, OLEDs have exceeded 60 lm/W power efficiency, and attained CRIs of 80 or better. Nevertheless, several significant technical and scientific challenges must be overcome before they become commercially viable for SSL applications. Some of these challenges include: 1. high cost of substrates (calculations suggest that the entire OLED must cost less than $100/m2); 2. low light outcoupling efficiency (calculations suggest that the light extraction efficiency should exceed 50%); 3. poor operational lifetime of blue-emitting materials, and 4. high cost of encapsulation (especially in the context of reel-to-reel manufacturing on flexible substrates).
According to the principles of the present teachings, a solid state light source is provided comprising a light pump outputting light energy; a waveguide optically coupled to the light pump for receiving the light energy; and a down-converter for converting the light energy from the waveguide to a lesser light energy.
Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.